This invention relates to a cylindrical storage battery provided with a spirally coiled electrode plate assembly, and more particularly to an alkaline storage battery for use as a drive power source of a vehicle, in which a lead terminal, electrically connecting a current collector, welded to an upper portion of the electrode plate assembly, to a sealing plate, is improved so as to enable charge and discharge with a large electric current and also to achieve excellent vibration-resistant properties.
Cylindrical storage batteries, represented by a nickel-cadmium storage battery and a nickel-metal hydride storage battery, have been widely used as a power source of a mobile phone, a laptop personal computer and so on because of their high reliability and easy maintenance. In recent years, there has been an increasing demand for the type of cylindrical storage battery suited for large-current discharge so as to be used as a power source of an electrically-operated tool, a power-assisted bicycle, an electric car and so on.
A cylindrical storage battery is formed by spirally winding a strip-shaped positive electrode plate and a strip-shaped negative electrode plate, with a separator interposed therebetween, to provide an electrode plate assembly, then by inserting this assembly, together with an electrolyte, into a casing made of metal, and then by closing an opening of this casing in a sealed manner.
In the type of alkaline storage battery used for discharging large current, a positive electrode plate and a negative electrode plate are wound in such a manner that an upper end portion of one of the positive and negative electrode plates projects upwardly from an upper end of an electrode plate assembly while a lower end portion of the other electrode plate projects downwardly from a lower end of the electrode plate assembly, and current collectors of a rectangular or a circular shape are welded respectively to the upwardly-projecting distal end and downwardly-projecting distal end of the two electrode plates at a plurality of spots, thereby enhancing the ability to collect electric current from the electrode plates. However, a resistance drop develops particularly at a lead terminal, connecting the electric collector to a sealing plate, thus inviting a problem that the operating voltage of the battery decreases, and besides there has been a possibility that the sealing plate and the lead terminal portion are disengaged from each other upon application of severe vibration and impact.
For example, FIG. 9 shows a horseshoe-shaped lead terminal 17 (disclosed in Japanese Utility Model Laid-Open Publication No. 58-74768) connected to a sealing plate 11 as shown in FIG. 10. The positioning of the lead terminal 17 is effected by loosely fitting its opening portion 17a on a projected portion 11a of the sealing plate 11 in contacted relation thereto, and a horseshoe portion 17b of the lead terminal 17 is connected to the sealing plate 11 by spot welding as shown in FIG. 10 which is a schematic, cross-sectional view. In this case, the lead terminal 17 is formed integrally with an electric collector 18.
In the structure shown in FIG. 9, however, when positioning the horseshoe portion 17b of the lead terminal 17 relative to the projected portion 11a of the sealing plate 11, this positioning can not be effected accurately unless the proximal end portion of the opening portion is held in contact with the projected portion 11a. Therefore, if even a slight displacement occurs, variations in the spot welded positions and an incompletely-welded condition are encountered. And besides, the lead terminal 17 has a horseshoe-shape, and therefore is not held against a side surface of the projected portion 11a, and therefore a load acts directly on the spot welded portions upon being subjected to vibrations, so that the spot welded portions are broken. Furthermore, the lead terminal 17 and the current collector 18 are formed into an integral construction, and the lead terminal 17 is formed on the outer peripheral edge of the current collector 18, and therefore particularly a current collecting portion 18a (of the current collector 18 connected to the electrode plate) remotest from the lead terminal 17 has a longer path of flow of electric current as compared with other current collecting portions 18b and 18c, and this causes the increase of an internal resistance of the battery.
In order to solve the above problems, the present invention provides a cylindrical storage battery which comprises current collectors, welded respectively to distal ends of strip-shaped positive and negative electrode plates projecting upwardly and downwardly respectively from a spirally coiled electrode plate assembly including the electrode plates and a separator, and a lead terminal connecting one of the current collectors to a sealing plate. In this storage battery, a hole is formed through one end portion of the lead terminal to be connected to the sealing plate, and this hole is fitted on a projected portion of the sealing plate. In one method, that portion of the lead terminal, surrounding this hole, is fixedly secured to the reverse surface of the sealing plate by laser welding. In another method, a plurality of projections or a ring-shaped projection are formed on that portion of the lead terminal surrounding the hole, and the projection or projections is/are secured to the reverse surface of the sealing plate. With this construction, the positioning of the lead terminal and the sealing plate relative to each other can be carried out easily, and therefore the welding connection can be effected in a stable manner, and besides this structure can withstand severe vibrations.
Further, a hole or a notch is formed through the other end portion of the lead terminal to be welded to the current collector, and that portion of the lead terminal, surrounding this hole, is held against a central portion of a flat plate portion of the current collector. In this case, the central portion is spaced from the center by a distance not larger than a half of the distance between the center and the outer peripheral edge. In one method, the portion of the lead terminal, surrounding the hole or the notch, is secured to the flat plate portion of the current collector by laser welding. In another method, a plurality of projections or a ring-shaped projection are formed on this portion surrounding the hole, and the projection or projections is/are secured to the current collector. With such construction, the paths of flow of electric current from current-collecting portions of the current collector, welded to the electrode plate, to the lead terminal, can be made shortest.
According to one aspect of the invention, there is provided a cylindrical storage battery comprising: an electrode plate assembly including a pair of strip-shaped positive and negative electrode plates and a separator which are spirally wound in such a manner that a distal end portion of one of the electrode plates projects upwardly from the electrode plate assembly while a distal end portion of the other electrode plate projects downwardly from the electrode plate assembly; a pair of upper and lower current collectors welded respectively to the distal end portions of the electrode plates, each of the current collectors being in the form of a flat plate of a substantially rectangular or a substantially circular shape; a metal casing containing the electrode plate assembly, the current collectors and an alkaline electrolyte therein; a sealing plate closing an upper end of the casing in a sealed manner; and a lead terminal electrically connecting the upper current collector to the sealing plate; wherein a projected portion is formed on a lower surface of the sealing plate, one end portion of the lead terminal has a hole fitted on the projected portion of the sealing plate, a projection is formed on that portion of the lead terminal surrounding the hole, and is welded to the lower surface of the sealing plate, and the other end portion of the lead terminal is welded to the upper current collector.
With such construction, the hole in the one end portion of the lead terminal is fitted on the projected portion of the sealing plate, and the projection on the lead terminal is welded to the lower surface of the sealing plate. Therefore, the displacement of the lead terminal and the sealing plate relative to each other will not occur, and therefore the welding connection between the two can be carried out in a stable manner, and besides even when a large impact and vibrations are applied to the battery, the welded portion, connecting the lead terminal and the sealing plate together, will not be broken, and therefore there can be provided the battery which exhibits the excellent reliability for a long period of time.
According to another aspect of the invention, there is provided a cylindrical storage battery comprising: an electrode plate assembly including a pair of strip-shaped positive and negative electrode plates and a separator which are spirally wound in such a manner that a distal end portion of one of the electrode plates projects upwardly from the electrode plate assembly while a distal end portion of the other electrode plate projects downwardly from the electrode plate assembly; a pair of upper and lower current collectors welded respectively to the distal end portions of the electrode plates, each of the current collectors being in the form of a flat plate of a substantially rectangular or a substantially circular shape; a metal casing containing the electrode plate assembly, the current collectors and an alkaline electrolyte therein; a sealing plate closing an upper end of the casing in a sealed manner; and a lead terminal electrically connecting the upper current collector to the sealing plate; wherein a projected portion is formed on a lower surface of the sealing plate, one end portion of the lead terminal has a hole fitted on the projected portion of the sealing plate, a projection is formed on that portion of the lead terminal surrounding the hole, and is welded to the lower surface of the sealing plate, one of a hole and a notch is formed through the other end portion of the lead terminal and a projection is formed on that portion of the lead terminal surrounding one of the hole and the notch, and is welded to the upper current collector.
With such construction, the hole in the one end portion of the lead terminal is fitted on the projected portion of the sealing plate, and therefore the lead terminal can be fixed, and also the projection around the hole of the lead terminal can be welded to the lower surface of the sealing plate in a stable manner, and the projection on the lead terminal is welded to the sealing plate, and therefore the strong welding can be achieved. And besides, the hole or the notch is formed through the other end portion of the lead terminal, and the projection is formed on that portion of the lead terminal surrounding this hole or notch, and is welded to the upper current collector, and welding current concentrates on this projection so that the upper current collector and the projection of the lead terminal can b welded together with a high strength. Thus, even when a large impact and vibrations are applied to the battery, the welded portion, connecting the lead terminal and the sealing plate together, and the welded portion, connecting the upper current collector and the lead terminal together, and will not be broken, and therefore there can be provided the cylindrical battery which exhibits the excellent reliability for a long period of time.
According to a further aspect of the invention, there is provided a cylindrical storage battery comprising: an electrode plate assembly including a pair of strip-shaped positive and negative electrode plates and a separator which are spirally wound in such a manner that a distal end portion of one of the electrode plates projects upwardly from the electrode plate assembly while a distal end portion of the other electrode plate projects downwardly from the electrode plate assembly; a pair of upper and lower current collectors welded respectively to the distal end portions of the electrode plates, each of the current collectors being in the form of a flat plate of a substantially rectangular or a substantially circular shape; a metal casing containing the electrode plate assembly, the current collectors and an alkaline electrolyte therein; a sealing plate closing an upper end of the casing in a sealed manner; and a lead terminal electrically connecting the upper current collector to the sealing plate; wherein a projected portion is formed on a lower surface of the sealing plate, one end portion of the lead terminal has a hole fitted on the projected portion of the sealing plate, a projection is formed on that portion of the lead terminal surrounding the hole, and is welded to the lower surface of the sealing plate, the upper current collector has a projection, the other end portion of the lead terminal has a second hole fitted on the projection on the upper current collector, and a projection is formed on that portion of the lead terminal surrounding the second hole, and is welded to the upper current collector.
With such construction, the hole in the one end portion of the lead terminal is fitted on the projected portion of the sealing plate, and therefore the lead terminal can be fixed, and also the projection around the hole of the lead terminal can be welded to the lower surface of the sealing plate in a stable manner, and welding current concentrates on the projection on the one end portion of the lead terminal. Thus, the strength of welding connection between this projection and the sealing plate increases. Further, the projection is formed on the upper current collector, and is fitted in the hole in the other end portion of the lead terminal, and therefore the lead terminal can be fixed. And besides, the projection around the hole in the other end portion of the lead terminal can be welded to the upper current collector in a stable manner, and welding current concentrates on the projection on the other end portion of the lead terminal, so that the strength of welding connection between this projection and the upper current collector increases.